This invention relates to a process for increasing the void percent of a hollow filament.
It is known in the art to produce hollow filaments by spinning multiple molten streams through a spinneret and coalescing the streams while they are still sufficiently tacky to form a bond. See Br. Pat. No. 1,106,263.
It is also known that freshly formed polyester structures may be permanently extended many times their length (up to 75 times) if the extending process is done under the proper conditions. See, for example, Pace U.S. Pat. No. 2,578,899. The extending process is carried out under low tension, at a slow rate and at a temperature 20.degree. C. to 60.degree. C. above the apparent minimum crystallization temperature.